1. Field of Invention
The present invention relates to printer positioning apparatus for use in high speed printers or the like and more particularly to a new and improved carrier moving rack and pinion apparatus in applications such as printers.
2. Description of The Prior Art
Prior art carrier moving mechanisms are known for use in both impact and ink jet type printers. In such mechanisms, a printing head is mounted on a carrier and movably attached to a guide rail. The carrier is moved either by a travelling or fixed motor which must position the printing head precisely in order to achieve the desired spacing between and among the characters printed upon paper or other medium.
Carrier moving mechanisms of the rack and pinion type all move the carrier by use of thrust force generated by a travelling motor rotating a pinion engaged in a rack mounted roughly parallel to one or more guide rails and to the exposed face of the medium upon which characters are to be printed. The principal advantage of rack and pinion type carrier moving mechanisms is the increased accuracy such devices allow in locating the printing head. Forward and reverse movement of the carrier mechanism is achieved by directional rotation of the pinion.
Prior art making use of rack and pinion type carrier moving mechanisms presents printer manufacturers with a dilemma. Designs utilizing close tolerances in the mechanism produce highly accurate character location. However, manufacturing to close tolerances is expensive. With use, machines so manufactured suffer greater wear and consequent mechanical break down and loss of accurate character placement. Conversely, machines manufactured to wider tolerances are cheaper to manufacture and suffer less mechanical deterioration. However, these advantages are obtained at the cost of lost precision in locating the printer head carrier mechanism. Hence, the rack, and pinion method of carrier movement and location, although attractive in addressing the problem of printer device placement, presents manufacturers with an inherently undesirable compromise among interrelated competing concerns: cost, accuracy of placement, and frequency of need for maintenance.
Prior U.S. Pat. No. 4,687,361 dated Aug. 18, 1987 by Kikuchi et al. represents an attempt to address and resolve this dilemma. For the purpose of the comparison, the distinctive characteristic of this prior art patent is that the rack is oriented on edge so that the teeth and the pinion engage about a vertical axis and the side of the rack opposite to the pinion rotation is engaged by a roller mounted on a rigid arm integrated with the moving carrier and driven by the rotating pinion. Moreover, the "edge wise" rack is longitudinally affixed to the frame of the printer roughly parallel to the guide rail means for the movable carrier such that the rack is adapted to be rotatable about one end of thereof with elasticity provided by a spring and the rack is made of polyamide resin and the like so that the rack can be rigid longitudinally thereof, as well as, flexible in a flex direction perpendicular to the longitudinal direction. This design permits manufacture of the rck and pinion mechanism from nonmetallic materials and to wider tolerances than in previous, rigidly affixed racks. In these latter respects, U.S. Pat. No. 4,687,361 achieves economies of manufacture similar to those of the present invention to be described hereinafter. However, a significant difference between the teachings of that prior patent and the present invention, is that the roller mounted on the rigid arm requires relatively tight dimensional tolerances which are costly. Also, the rigid arm design does not compensate for wear between the pinion and rack which may result in inaccurate positioning of the carrier and its related printing head. In addition the "edge wise" orientation of the rack and pinion action in U.S. Pat. No. 4,687,361 is conducive to making the mechanism susceptible to contamination from the printer correction process.